1. Field of the Invention
The present invention relates to an apparatus controlled by a microprocessor, and more particularly to an apparatus controlled in a predetermined safe state even when the microprocessor is in a faulty state.
2. Description of the Prior Art
As an example of an apparatus controlled by a control circuit using a microprocessor, there is a forced flow air heating apparatus, called an FF type heating apparatus. In such an apparatus, if the microprocessor goes wrong, the apparatus is controlled in an abnormal condition and thus might be in an extremely dangerous state. Therefore, it is demanded to detect a fault of the microprocessor in such a case and to control the apparatus so as to protect it from the danger. Nevertheless, a conventional apparatus of this type is not controlled under a safety state since it does not respond to a fault of the Summary of the Invention.
Accordingly, an object of the invention is to provide an apparatus controlled by a microprocessor which is to controlled in a safe state when the microprocessor is out of order.
According to an embodyment of the invention, there is provided an apparatus controlled by a microprocessor which has an integrated microprocessor, a detecting circuit and a protecting circuit. The integrated microprocessor includes a time counting logic circuit supplied with a reference input signals for counting the input signals and producing a first signal, a main control logic for receiving the first signal for producing a second signal and at least one output signal for controlling the apparatus, and an AC signal generating logic for receiving the first and second signals in order to produce an AC signal and a third signal whereby the AC signal is produced at a first operation state of the microprocessor and the AC generating logic has first and second levels repeated alternately with the third signal produced by a second operation state of a microprocessor and wherein the third signal has one of either the first or second levels for a predetermined period of time. The detecting circuit detects the AC signal and produces a first detection signal and detects the third signal and produces a second detection signal. The protecting circuit is connected to the detecting circuit and applies a fourth signal to the apparatus for putting the apparatus in a safety condition when the protecting means receives the second detection signal.